After 12 years, ABBA songfest “Mamma Mia!” will leave the roomy Winter Garden this fall for more modest digs at the Broadhurst, perhaps to make room for “Rocky das Musical.” Photo: Bruce Glikas/FilmMagic

‘mamma Mia!” is on the move.

After 12 years and 5,000 performances, “Mamma Mia!” is decamping from the Winter Garden to the Broadhurst in the fall.

The move is a tacit acknowledgment that the show is beginning to show some weakness at the box office, though hardly enough to close it outright.

With more than 1,500 seats, the Winter Garden is one of Broadway’s largest — and most-sought after — theaters. The popular ABBA musical has had trouble filling all those seats in the last couple of years, and so a move to the smaller, 1,186-seat Broadhurst makes sense.

Sources say the transfer will allow the Shubert Organization, Broadway’s biggest landlord, to put the new “Rocky” musical into the Winter Garden next season.

Based on the 1976 Sylvester Stallone movie, “Rocky das Musical” received strong reviews last fall in Hamburg, Germany. The score is by Lynn Ahrens and Stephen Flaherty (“Ragtime”) and the script is by Stallone and Tom Meehan (“Annie”). Critics applauded the staging, by Alex Timbers (“Bloody Bloody Andrew Jackson”), especially a boxing sequence during which the regulation-size ring soars out over the audience.

(The Winter Garden was home for nearly 20 years to another soaring set piece — the gigantic tire that transported Grizabella to the Heaviside Layer in “Cats.”)

“Rocky das Musical” cost $20 million to stage in Germany. Sources say the price tag could hit nearly $30 million in New York. With so much money to recoup, the show would inevitably have to land at one of Broadway’s largest theaters.

“Mamma Mia!” is one of the most profitable stage musicals of all time. It cost $10 million to stage at the Winter Garden, and has grossed more than $2 billion from productions around the world.

Production sources say the show won’t be chopped down for the Broadhurst. All that’s being reduced, I’m told, is the rent.

Craymer says the move will “allow us to delight audiences on Broadway for many years to come.”

Producers have tried to nudge Craymer out of the Winter Garden before. Nick Starr, executive director of the National Theatre of Great Britain, suggested last year she give up the Winter Garden so the National could put its Tony-winning “War Horse” there.

But Craymer wouldn’t hear of it, and wound up having one of her most profitable summers ever.

Embarrassed that he dared to suggest “Mamma Mia!” was running out of steam, Starr later sent Craymer a very large bouquet of flowers with a note that read: “From your friends at the National Theatre.”

But “Mamma Mia!” struggled during the winter, and right now you can pick up discounted tickets from hawkers in Times Square.

Craymer is likely to reap publicity with a big bash celebrating her move to the Broadhurst.

She might even take a page out of the David Merrick playbook. He moved his hit show “42nd Street” three times in the 1980s — from the Winter Garden (to make way for “Cats”) to the Majestic and finally (to make way for “The Phantom of the Opera”) to the St. James.

Each time it moved, Merrick had his cast, in full costume, tap dance and sing “We’re in the Money” through Times Square, to the delight of tourists and photographers.

Every time “42nd Street” traveled, its box office improved, and the show didn’t expire until its 3,486th performance.

Maybe Craymer should stage an ABBA hit parade down Broadway. The grand marshals could be Benny Andersson and Bjorn Ulvaeus.

That should keep the cash registers ringing at the Broadhurst for a nice long time.